Exemplary embodiments of the present invention relate to a semiconductor device fabrication technology, and more particularly, to an image sensor and a method for fabricating the image sensor.
Image sensors are semiconductor devices which transform an optical image into electrical signals, and a CMOS image sensor (CIS) is widely used. An image sensor includes a color filter array (CFA) to acquire/detect a color image. Herein, the color filter array is composed of three different colors of filters, which are red, green and blue.
FIG. 1 is a cross-sectional view illustrating a conventional image sensor.
Referring to FIG. 1, the conventional image sensor includes a blue pixel active region 20B, a green pixel active region 20G, and a red pixel active region 20R that are defined by an isolation layer 12 formed over a substrate 11. Each of the blue pixel active region 20B, the green pixel active region 20G, and the red pixel active region 20R includes an optical sensor 15, which is formed by a junction of a P-type impurity region 14 and an N-type impurity region 13, and a transfer gate 16. A protective layer 17 is disposed over the substrate 11 including the transfer gate 16, and a color filter array 18 of three colors, which are red R, green G, and blue B, corresponding to the optical sensor 15 of each pixel are disposed over the protective layer 17. A condenser 19 is disposed over the color filter array 18.
The image sensor including the color filter array 18, which is described above, has excellent color separation characteristics. However, in transmission of different colors of light, in case of green G, about 50% of light transmits in the color filter array 18, and in case of red R and blue B, about 25% of light transmit. In short, the image sensor has a drawback of low quantum efficiency.
To prevent the quantum efficiency from being deteriorated due to a color filter array in an image sensor, an image sensor using not the color filter array but the difference in absorption of the light according to its wavelength has been developed.
FIG. 2 is a cross-sectional view illustrating a modified conventional image sensor.
Referring to FIG. 2, the modified conventional image sensor includes an optical sensor 15 which has a structure that a P-type impurity region 14 and an N-type impurity region 13 are alternately disposed multiple times. Herein, blue B, green G, and red R colors of light in order are detected by progressively deeper regions of the N-type impurity region 13 in the optical sensor 15.
The modified conventional technology having the above-described structure may improve the quantum efficiency characteristics because it does not use a color filter array. However, since the optical sensor 15 has a complicated structure, the image sensor may be relatively difficult to manufacture and production yield of image sensor may suffer. Also, since colors are separated by stacking three photodiodes per pixel, that is, junctions of the P-type impurity region 14 and the N-type impurity region 13, according to the modified conventional technology, the light absorption depth may overlap and it may be difficult to separate colors. Therefore, an image sensor that may improve both color separation characteristics and quantum efficiency characteristics simultaneously is useful.